A. Field of the Invention
The present invention relates to an improvement in a process for making sodium dichloroisocyanurate. In particular, the present invention relates to an improvement in a process for making sodium dichloroisocyanurate wherein a hazardous by-product NCl.sub.3 is removed.
B. Description of the Prior Art
Sodium dichloroisocyanurate, hereinafter sometimes called SDCC for the sake of brevity, is widely used today as an important source of active chlorine in solid detergent and bleaching compositions, and in the chlorination of water, especially swimming pools. This compound is desirable for these uses because it remains relatively stable under both ambient storage conditions and in the absence of substantial amounts of moisture. Furthermore, it is very soluble in water and will readily give off active chlorine when placed in an aqueous slurry.
One known process for preparing SDCC is to react together trichloroisocyanuric acid, cyanuric acid and sodium hydroxide in an aqueous solution to form the desired SDCC and H.sub.2 O. This process is represented by the following equation: ##STR1## However, in this process several by-products may be formed. The most troublesome of these possible by-products is nitrogen trichloride (NCl.sub.3). This compound is a volatile yellow oil which may readily explode in either the liquid or vapor phase when subjected to shock, organic material or temperatures of 60.degree. C. or higher. Therefore, the presence of appreciable amounts of NCl.sub.3 in the SDCC reactor may be quite hazardous.
Another known process for producing SDCC is reacting dichloroisocyanuric acid with sodium hydroxide in an aqueous reaction medium as taught in U.S. Pat. No. 3,299,060, issued to Kovalsky et al. on Jan. 17, 1967. Still another is reacting one mole of trisodium isocyanurate with two moles of trichloroisocyanuric acid to produce three moles of SDCC.
In the past, it was necessary to further process the SDCC reaction mixture of the above reactions to remove these undesirable quantities of NCl.sub.3. This procedure was time-consuming and costly. Further, it was necessary to shut down the SDCC processes at periodic intervals to remove accumulations of this explosive compound from the reactor and other processing equipment.
Therefore, a need exists in the SDCC industry to find a process improvement to the above reaction which would result in the production of a SDCC reaction mixture that is substantially free of nitrogen trichloride, thereby helping eliminate the need for further processing of the product. Also, such an improvement would be even more beneficial if it also aided in the elimination of the periodic shutdown in the process. It is believed that the present invention solves this need.
U.S. Pat. No. 3,184,458, issued to Frazier on May 18, 1965, discloses the employment of an inert purge gas to remove NCl.sub.3 in the production of trichloroisocyanuric acid. However, the process discussed in that patent and the present process are far different because that prior art process employs a specific chlorination reaction whereas the present invention does not chlorinate with gas. Still further, the process taught therein employs an inert purge gas after the reaction is over, thereby requiring separate stripping apparatus, or in combination with the chlorine gas during the reaction.